What does it actually mean?

What is that "YKK" that you see on your zippers? 10 codes explained

Have you noticed "YKK" stamped on your zippers or that "RSVP" on an invitation? What does the mysterious "SSSS" on your boarding pass mean? These little letters and codes are everywhere, but if you stop and think about it, there are plenty whose meaning we don’t really know. Behind many of them are surprising stories, foreign languages, old technologies, and even a few myths. Here are 10 everyday codes and abbreviations you’ve probably seen countless times without knowing what they actually mean.

You’ve probably noticed that almost every zipper on your clothes has the letters "YKK" stamped on it. But have you ever wondered what those three letters actually mean?

They stand for Yoshida Kogyo Kabushikikaisha, the name of the huge Japanese manufacturing company that produces roughly half of the world’s zippers. Founded by Tadao Yoshida in Tokyo in 1934, the company became a global zipper powerhouse, and its familiar YKK logo now appears on the pull tabs of zippers around the whole world.

Every time you receive an invitation to a wedding, birthday, or other important event, there it is: "RSVP" in all caps. But what do those four letters actually mean?

The initialism comes from the French phrase Répondez s'il vous plaît, meaning "please reply," or literally, "respond, if it pleases you." The request for a response originated in Europe and was adopted by the American elite, who embraced French court etiquette in the 18th century, preserving the French expression. Today, RSVP has become a practical yet elegant way to ask guests to confirm whether they’ll attend, helping hosts know how many people to expect.

One of the most famous codes in the world, SOS is the quintessential emergency signal, recognized across languages and around the globe. But what do those three letters actually mean?

Contrary to popular belief, SOS doesn’t stand for "Save Our Souls" or "Save Our Ship." That misconception took hold in the early 1910s and became widespread after the sinking of the Titanic in 1912. In reality, the letters don't stand for any words; the signal was chosen internationally at the Berlin Radio-Telegraphic Conference in 1906 and went into effect in 1908 because of its distinctive Morse code sequence. Three dots, three dashes, and three dots (... --- ...) create a simple rhythm that is easy to send and recognize during an emergency.

Have you ever noticed a strange "SSSS" code on your boarding pass? Perhaps you saw it the same day you were pulled aside for an extra security check before boarding. That’s no coincidence.

It stands for "Secondary Security Screening Selection". It’s a designation placed on some boarding passes by security authorities, such as the TSA, indicating that the passenger has been selected for additional screening, which can include a pat-down, baggage inspection, or explosive-residue swab. But seeing SSSS doesn’t necessarily mean there’s anything suspicious. Passengers can be selected based on certain travel or booking criteria, but they may also be chosen at random. If you see SSSS on your boarding pass, give yourself an extra 30 to 45 minutes, since the additional screening can take more time.

In countless history books, timelines, and educational materials, we see the abbreviations B.C. and A.D., or their modern alternatives, B.C.E. and C.E. But why do we use them, and why are there two versions?

We use these abbreviations to date historical events, counting years backward before the traditional birth of Jesus and forward after it. B.C. means "Before Christ," while A.D. stands for Anno Domini, a Latin phrase meaning "in the year of our Lord." The modern alternatives use more secular language: B.C.E. means "Before the Common Era," and C.E. means "Common Era." Both systems use the same year numbers and the same calendar points; the difference is simply whether the terminology has an explicitly Christian reference.

At the end of a U.S. mailing address, right after the city and state, we have the familiar ZIP Code. We’ve been using it for decades, but many people still don’t know exactly what those three letters stand for.

"ZIP" stands for "Zoning Improvement Plan." The U.S. Postal Service introduced the system in 1963 as mail volumes continued to rise, making faster, more efficient processing more and more important. These codes divided the country into geographic areas, giving postal workers a more organized way to sort and deliver mail. They also became an important part of the Postal Service’s growing use of automated sorting machines, helping mail literally "zip" through the system.

Have you noticed that whenever you forward an email, the abbreviations CC and BCC are right there? These familiar letters actually come from a time long before email.

CC stands for "Carbon Copy" and means other recipients can receive a copy while their addresses remain visible. BCC, or "Blind Carbon Copy," also sends a copy, but hides the recipient’s address from everyone else. The terms date back to the days of typewriters and carbon paper, which allowed people to make duplicate copies of a letter as they typed. A "CC" notation showed who else received a copy, while a "BCC", or blind copy, kept that additional recipient in secret.

"P.S." is undoubtedly one of the most familiar abbreviations used in letters and emails around the world. But do you know exactly what it means and why we use it?

Before computers and smartphones made it easy to edit text, writing a letter by hand meant that forgetting something often meant adding it afterward. "P.S." comes from the Latin post scriptum, meaning "written after." Adding it at the bottom of a letter gave you a simple way to include an extra thought or piece of information without rewriting the entire page.

You’ve probably used your debit card PIN countless times. Most people know theirs by heart, but how many of us actually know what those three letters stand for?

"PIN" stands for Personal Identification Number, a security code used to verify that the person using a card or accessing an account is authorized to do so. It dates back to 1966, when the PIN system was developed as part of efforts to create an automated cash dispenser. The following year, in 1967, the first ATM was introduced for public use. But there’s one small mistake many of us make without realizing it: "PIN number" is redundant, because the "N" already stands for "Number."

Whenever we read an explanation or definition, we often come across "e.g." and "i.e.", especially in dictionaries and reference books. They may look similar, but what do those letters actually stand for?

"E.g." is short for the Latin exempli gratia, meaning "for example." On the other hand, "i.e." comes from the Latin id est, meaning "that is" or "in other words." The two are easy to confuse, but they serve different purposes. Use "e.g." when you want to give a few examples of something, such as "I like tropical fruits, e.g., mangoes and pineapples." And "i.e." when you want to clarify or restate exactly what you mean, such as "I am a vegan, i.e., I do not eat any animal-based products."

Beloved lyrics

"For what is a man?": Some of the wisest lyric lines ever written

Paul Anka was terrified when he sat down to write the lyrics for a song that Frank Sinatra would be singing. Jokingly, he started with a dramatic, "And now, the end is near…" The rest is history. Who are the people who pen the words that others will spend decades repeating? How did they come up with words so precise and true that listeners would compare them with those of great philosophers? Here are 10 of people’s favorite lyrics of all time, decoded.

"For what is a man? What has he got? If not himself, then he has naught." The melody of "My Way" wasn't originally American. It began as a French song called Comme d'habitude, a number about a couple stuck in a stale marriage. Paul Anka heard it on the radio while in France and bought the rights on the spot, before he had any use for it.

That use arrived at a dinner in Miami, when Sinatra told him, almost in passing, that he was quitting the business. Anka flew home, sat down at a typewriter, and spent one night writing lyrics as if Sinatra himself were speaking them. Sinatra recorded it in two takes and later called it his "national anthem," and many agreed; Anka had written the exact words one wants to belt while closing an episode of their life.

In "Beautiful Boy (Darling Boy)," John Lennon wrote: "Life is what happens to you while you are busy making other plans." But the phrase originated with American writer and cartoonist Allen Saunders, who published it in a 1957 issue of Reader's Digest ("Life is what happens to us while we are making other plans").

The line outlived everything else about the song, repeated at graduations and eulogies for decades since. Lennon was murdered shortly after the album's release, which means the song now carries a weight of hindsight neither he nor his listeners could have intended at the time.

"How many roads must a man walk down before you call him a man?" A young Bob Dylan wrote "Blowin' in the Wind" in 1962. He later claimed he wrote the entire song in about ten minutes at the Gaslight Cafe in Greenwich Village, borrowing its melody from the old spiritual "No More Auction Block." He was twenty-one, barely a year into his New York career, and insisted at the time it wasn't a protest song at all.

The song never answers its questions, but keeps asking them. First published in the folk magazine Broadside in May 1962, it became the unofficial anthem of the civil rights and antiwar movements once Peter, Paul and Mary's cover shot to number two on the charts in 1963.

"... is equal to the love you make." This is the last song the four Beatles ever recorded together, and Paul McCartney built it deliberately as a farewell. He gave Ringo Starr his only drum solo in the band's history, a fight McCartney had to win through what he called "gentle persuasion," since Starr detested solos on principle.

For the closing line, McCartney said he'd been thinking about Shakespeare, who often ended a scene with a rhyming couplet so the audience would know it was truly over. Even John Lennon, who generally disliked the Abbey Road medley and rarely praised his old partner's work by 1980, admitted the closing thought was "a very cosmic, philosophical line."

"... but it’s better than drinking alone." "Piano Man", by Billy Joel, narrates a song in which the character is real. Joel wrote it about the six months he spent playing piano under the fake name "Bill Martin" at a Los Angeles lounge called The Executive Room. Even the waitress "practicing politics" was Elizabeth Weber, the woman who'd soon become his wife.

Joel wrote it while hiding out from a record label he was desperate to escape after his debut album flopped. It became a bittersweet anthem that many people love singing with others; it seems like, as the song suggests, singing sorrows together at the bar is better than feeling them at home.

The whole song "Both Sides Now," by Joni Mitchell, is often quoted as a deeply philosophical observation of life. It concludes that some mysteries of life are as unknowable as the clouds, or love, despite accumulating experience.

When she wrote it, Mitchell had recently given up a daughter for adoption after being left by the child's father. She was twenty-three, mid-flight, after a passage in Saul Bellow's novel Henderson the Rain King described its narrator looking down at clouds from an airplane, something human eyes had only been able to do for a few decades. Judy Collins released it first in 1967 and won a Grammy for it; Mitchell's own version didn't appear until her 1969 album Clouds.

Kris Kristofferson’s song, "Me and Bobby McGee", contains one of people’s favorite quotes from song lyrics. Its title came from producer Fred Foster, who suggested Kristofferson write a song about his colleague's secretary, Barbara "Bobbie" McKee.

Its most quoted idea about freedom and loss was inspired, Kristofferson later said, by the final scene of Fellini's La Strada, in which a man realizes too late what he threw away. Roger Miller released it first, but it was Janis Joplin's posthumous 1971 recording, finished mere days before her death, that turned it into a number one hit and an accidental epitaph.

"... and I'm getting older too." Nicks says she wrote "Landslide" in about five minutes, sitting in a rented house in Aspen while her partner and musical collaborator, Lindsey Buckingham, was on tour rehearsing with the Everly Brothers. The song's real subject isn't romance, but the vertigo of watching time pass. She was twenty-seven, broke, working as a waitress and a cleaner, and their duo album had just been dropped by its label.

Looking at the snow on the Rockies, she found herself deciding whether to keep chasing music at all. Three months later, Mick Fleetwood heard Buckingham's guitar work on a demo and invited the pair into Fleetwood Mac, which changed their lives. The song has now aged into an anthem for anyone facing a hinge point in their own life.

"You can't always get what you want, but if you try sometime you'll find you get what you need." Mick Jagger sketched this one alone on an acoustic guitar, calling it "one of those bedroom songs." It closed 1969's Let It Bleed just as the decade's peace-and-love optimism was cracking.

The song is upbeat and simple, and unexpectedly insists on an idea of acceptance or surrender that has more to do with Stoic philosophy than with pop rock optimism. But the listeners liked it, and many quote it often.

"...that's how the light gets in." Leonard Cohen worked on "Anthem" for roughly a decade, discarding draft after draft, before it finally appeared on his 1992 album The Future. He wasn't a man given to explaining his own lyrics, having spent years training as an ordained Zen Buddhist monk and generally preferring silence to self-analysis.

But "Anthem" has the clearest statement of a philosophy he'd circled his entire career: that brokenness can give way to grace. It has since been invoked by human rights activists, quoted at protests, and performed at civic ceremonies.